A technique of generating an instruction corrected to provide a trajectory that is a target response result of a control target has been used hitherto in order to remove an error such as a response delay caused by characteristics of the control target. In particular, a technical field in which a cutting operation or turning operation is performed on a non-circular workpiece uses a technique of correcting an instruction position of a tool in order to achieve a high-speed and high-accurate machining operation. Such a technique is disclosed in, for example, Patent Literatures 1 to 3.
Patent Literature 1 discloses a technique for a cam grinder that machines a cam surface into a desired cam profile through a plurality of times of grinding operations on the basis of control data representing a relationship between a grinding wheel feeding amount and a main spindle rotation angle stored in advance in correspondence with the desired cam profile. In this technique, the difference between the grinding wheel feeding amount of the actual grinding operation and the grinding wheel feeding amount of the control data is obtained and the control data used in the next grinding operation is corrected on the basis of this difference.
Patent Literature 2 discloses a technique in which a machining error in a device that machines a non-circular workpiece is corrected by controlling a movement of a tool synchronized with the rotation of the workpiece. For this technique, a position of the tool that has moved in accordance with the instruction position that is the same as or similar to the target position of the tool is detected. Then, among the amplitude ratio, the phase difference, and the offset difference between the target position and such a detected position, at least the amplitude ratio and the phase difference are obtained. Subsequently, among three kinds of processing, i.e., processing that enlarges/reduces the instruction position on the basis of the amplitude ratio, phase-shift processing based on the phase difference, and processing that changes the offset of the instruction position on the basis of the offset difference, at least the enlargement/reduction processing and the phase-shift processing are performed to obtain a corrected instruction position.
Patent Literature 3 discloses a technique for a non-circular workpiece controlling method in which a machining tool is controlled such that a non-circular workpiece moves to the data position in accordance with the angle of a mounted main spindle, and the machining tool feeding position is controlled in synchronization with the rotation of the main spindle. For this method, first target input position Fourier transformation data is obtained by Fourier-transforming target input position data for controlling the position of the machining tool, an actual movement amount obtained by controlling the position of the machining tool is detected as actual movement amount data, first actual movement amount Fourier transformation data is obtained by Fourier-transforming the detected actual movement amount data, a transfer function as a ratio between the first target input position Fourier transformation data and the first actual movement amount Fourier transformation data is calculated, second correction target input position Fourier transformation data obtained by correcting the first target input position Fourier transformation data is calculated by the transfer function, second target input position data is newly obtained by inverse Fourier-transforming the second correction target input position Fourier transformation data, a transfer function as a ratio between second target position Fourier transformation data obtained by Fourier-transforming second target position data obtained from the second target input position data and second actual movement amount Fourier transformation data obtained by Fourier-transforming the second actual movement amount data is repeatedly obtained, third target input position Fourier transformation data is newly calculated by correcting the first target input position Fourier transformation data on the basis of the transfer function, and third target input position data is newly obtained by inverse Fourier-transforming the third target input position Fourier transformation data. In this way, the operation is controlled by the use of these data items.